The present invention relates to tennis rackets.
It is known to manufacture a tennis racket having a handle portion, a frame portion adapted to have strings mounted thereon and a throat portion connecting the handle and the frame portion. It is also known to provide an insert in the throat portion, connected to the same and adapted to have secured thereto at least some of the strings normally mounted in the frame.
It has been known to manufacture tennis rackets of laminated wood. However, recently the tennis rackets are manufactured from synthetic plastic material, metal or any other material so as to completely or at least substantially exclude (i.e. substitute) wood.
The strings are known to be manufactured of lamb's gut (i.e. which is quite expensive) or oil-filled plastic capillaries.
The above-mentioned some strings extend through the insert outwardly away therefrom towards the respective sections of the throat portion and are secured thereto. The number of these strings (i.e. extending through the insert) varies depending upon the actual construction of the tennis racket in general and the insert in particular. As a rule, there are between ten and sixteen of such strings on the tennis rackets of this type (i.e. having the inserts).
The inset is usually made of synthetic plastic material, which preferably has a substantially low cold deformation characteristics, for example, a suitable type of polyamide.
The tennis rackets of this type are characterized by the fact that a normal hit (i.e. so-called "sweet spot" or "sweet point") of a ball occurs not right in the center of the frame portion, but somewhere between the center of the frame portion and the throat portion. Usually, the section of the strings which hits the ball may be determined by relation between the position of the frame portion of the racket and the center of gravity of the tennis racket, which usually is located in the area of the throat portion. This rule is long since known. Such tennis rackets have been known since thirties. The first examples of these tennis rackets used to have an extremely enlarged frame portion and a respectively reduced handle portion. Even to this day, there are some suggestions (e.g. German Offenlegungsschrift No. 2 546 028) to provide a tennis racket with a relatively large frame portion. Such a tennis racket, obviously, has some advantages, e.g. a player hits the ball with a comparatively light impact. However, such a tennis racket with a relatively large frame portion encounters a correspondingly increased air resistance which at least prevents a fast game. Another advantage of such a tennis racket resides in the fact that the geometric center of the frame portion is located close to the so-called "sweet point". This feature ensures that the elastic deflection (i.e. yielding) of the strings (which occurs in response to the impact of the ball onto the strings) normal to the general plane of the frame portion is substantially more uniformly distributed as opposed to the tennis rackets with the comparatively smaller frame portions. In this case, in response to the impact of the ball the elastically yieldable strings develop a counterforce which "strikes" the ball back. However, due to the rigidity of the insert, the strings which are secured thereto develop a component counterforce which is directed at a small angle relative to the ground to the general plane of the frame portion. Thus, should a player locate the frame portion so as to meet the ball perpendicular to the general plane of the frame portion (i.e. which is the most effective hit) then the ball reflects from the strings not perpendicular thereto (as desired) but at an angle relative to the normal to the general plane of the frame portion. This deflection from the desired direction of the ball flying from the tennis racket is determined by the above-mentioned component of the counteractive force of the elastically yieldable strings. Obviously, any deflection of the ball may significantly affect the eventual result of a tennis game.